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RFC 3848 / MAIL TRANSMISSION TRACE

Use the LMTP family for local delivery

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LMTP means Local Mail Transfer Protocol. It is a separate protocol for agreed delivery arrangements, often between a queue manager and a delivery agent. RFC 3848 registers four LMTP transmission types.

DIAGRAMRead RFC section 1 ↗
RFC 3848 · § 1EXAMPLE
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Use the LMTP family for local deliveryThree LMTP scenes. A queue manager uses configured LMTP delivery with LHLO to a delivery agent, not public TCP25; base type LMTP. Separate afterDATA outcomes return one reply per previously successful RCPT in command order:250for first,450for second. A four-cell matrix maps no properties, AUTH only, strong STARTTLS only, both to LMTP,LMTPA,LMTPS,LMTPSA. Distinct receptions, not negotiations by header. This bounds the contextual2033mechanism.LMTP is a separate configured delivery protocolFour separate receptionsLMTPAUTH: no successSTARTTLS: no layerLMTPAAUTH: successSTARTTLS: no layerLMTPSAUTH: no successSTARTTLS: strong layerLMTPSAAUTH: successSTARTTLS: strong layerA header label does not negotiate a protocol
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Read all four LMTP labels.

The matrix compares four distinct receptions: neither successful property gives LMTP; AUTH gives LMTPA; STARTTLS gives LMTPS; both give LMTPSA. No action is negotiated merely by writing a label.

Source for this drawing: RFC 3848 · Read RFC section 1 ↗

Protocol participantThreat or exceptionProtocol controlSimplified drawings · precise section references
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A message needs an address.

Think of a packet as a small addressed envelope. Devices pass it onward; transport protocols decide what delivery promises an application gets.

Helpful first, if these ideas are unfamiliar

RFC 5321 SMTP RFC 5322 Email message format RFC 3207 SMTP STARTTLS

These pictures are analogies to help you learn. The linked RFC explains the actual rules.

Related RFCs and changes

“Updates” changes part of an earlier RFC. “Obsoletes” replaces it. This list shows selected related documents.

KEY POINT

Select the protocol family first, then its successful properties.

  • RFC 2033 §§1 and 4.1 describe prior arrangement, forbid LMTP on TCP port 25, and replace EHLO with LHLO. It is not just another spelling of ESMTP.
  • The four registrations are LMTP, LMTPA, LMTPS and LMTPSA. A and S retain the successful AUTH and strong STARTTLS meanings.
  • RFC 2033 §4.2 returns one post-DATA reply for each previously successful RCPT command, in command order. The two recipient outcomes shown are fictional.
  • RFC 3848’s parenthetical LSMTPS/LSMTPA spelling is inconsistent with its defined LMTPS/LMTPA keywords; use the defined registrations, not invented extra tokens.
DETAILS

LMTP context comes from RFC 2033; this is not a complete LMTP implementation.

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